HT to @wdormann here - somebody has backdoored the open source project XZ which has downstream impacts.
For example, although OpenSSH doesn’t use XZ, Debian patch OpenSSH and introduced a dependency which translates as the XZ changes introducing a sshd authentication bypass backdoor it appears.
One dude bothered to investigate in his free time about why ssh was running slow, so it was caught fairly early - i.e. hopefully before distros started bundling it.
As I said, the impact here will be very limited due to how quick it was caught. Everybody owes the finder a beer.
NOTE: THIS IS AN ATTEMPT AT INCLUDING A BACKDOOR. THIS IS LEFT FOR HISTORICAL PURPOSES ONLY AND MUST NOT BE DONE. Please sync xz-utils 5.6.1-1 (main) from Debian unstable (main) Hello! I am one of the upstream maintainers for XZ Utils. Version 5.6.1 was recently released and uploaded to Debian as a bugfix only release. Notably, this fixes a bug that causes Valgrind to issue a warning on any application dynamically linked with liblzma. This includes a lot of important applications. This cou...
Originally reported on Google Code with ID 342 What steps will reproduce the problem? 1. Testcase is attached. Compile with GCC with -fsanitize=address option. 2. Run. 3. What is the expected outpu...
Back in 2022 a host of characters appeared and basically bullied the creator of the XZ project to hand it over to somebody else - at the time the guy cited mental health issues around not updating the project quickly.
At the time he was already talking about maybe handing over to the account who years later introduced the backdoor.
In mid 2023 said account introduced a change to Google’s OSS Fuzzer to weaken detection for XZ.
Somebody played a years long game of Jenga and lost.
Before everybody high fives each other, this is how the backdoor was found: somebody happened to look at why CPU usage had increased in sshd, and did all the research and notification work themselves. By this point the backdoor had been there for a month unnoticed.
I’ve made the joke before that if GCHQ aren’t introducing backdoors and vulns in open source that I want a tax refund. It wasn’t a joke. And it won’t be just be GCHQ.
Another two thoughts on XZ -
- sshd itself has no dependency on the XZ utils library. The streams got crossed in a way I don’t think anybody understood (except the threat actor).
- had that backdoor been performant with sshd, I don’t think anybody would have spotted it.
The way this played out opens a window of opportunity to go back and look at both issues.
Really good timeline of what is known to have happened so far. It looks like the rogue developer deliberately introduced a vulnerability in other package, too - I haven’t seen anybody else mention this.
Reading the dev’s GitHub history, they’ve been making changes to other open source projects too around compression. It also appears they/somebody involved has other accounts, too.
https://boehs.org/node/everything-i-know-about-the-xz-backdoor
How far the rabbit hole goes - back in 2021 they deliberately introduced a risky change in the compression library libarchive. Nobody noticed. This is shipped in a ton of systems:
https://github.com/libarchive/libarchive/pull/1609
Whoever the threat actor is knows what they are doing as they’ve gone after chained dependencies around compression.
Added the error text when printing out warning and errors in bsdtar when untaring. Previously, there were cryptic error messages when, for example in issue #1561, the user tries to untar an archive...
If anybody thinks this kind of thing is unique, it isn’t.
Example - CVE-2021-44529 in Ivanti Endpoint Manager. The cause?
Backdoor in open source code, was there for 7 years.
XZ Embedded Linux kernel module for IoT devices, 10 days ago had a change submitted to add Jia Tan (backdoor author) as a maintainer.
https://lore.kernel.org/lkml/202403201[email protected]/
Linux kernel documentation: https://docs.kernel.org/staging/xz.html
The GitHub repository for XZ Embedded kernel module has also been disabled: https://github.com/tukaani-project/xz-embedded/
Kevin Beaumont
CassandraVert